1. Technical Field
The present invention generally relates to a propylene oligomer, a lubricating oil additive derived from the propylene oligomer, and lubricating oil composition containing same.
2. Description of the Related Art
There is increasing evidence that certain synthetic and natural chemicals may act on the endocrine system. For example, certain synthetic and natural chemicals can act as agonists or antagonists to cellular receptors such as estrogen receptors, androgen receptors, and thyroid hormone receptors. Agonists bind to cellular receptors and trigger a response, whereas antagonists block the action of an agonist. Natural and synthetic chemicals can interfere in various ways with naturally occurring hormones. These chemicals can be called endocrine disruptors. For example, endocrine disruptors can (1) mimic naturally occurring hormones by binding to hormone receptors, (2) block the binding of naturally occurring hormones to their respective hormone receptors, (3) alter natural levels of hormones, (4) increase or decrease natural hormone levels, and (5) interfere with the way hormones travel through the body.
Chemicals that interfere with the normal functioning of estrogens and estrogen receptors provide an example of endocrine disruptors. Certain chemicals (called pseudo-estrogens) and natural estrogens can share a common mechanism of action. In normal cases, estrogenic activity is produced by binding natural estrogen to an estrogen receptor (ER) within the nucleus of the cell, followed by transcriptional activation of target genes. This transcriptional activation can occur through the binding of the estrogen receptor to promoter sequences within the regulatory region of the target genes. When endocrine disruptors are present that mimic natural estrogens, the endocrine disruptor can bind to the ER causing transcriptional activation by the ER even though no natural estrogen is present. Similarly, antiestrogenic activity is produced by endocrine disruptors which bind to ERs, but which do not subsequently activate the occupied ER as well as natural estrogen. Finally, selective estrogen receptor modulators (SERMs) bind to ERs, but subsequently activate cellular responses that differ from those activated by the natural estrogens. In general, all but a very small number of molecules that bind to ERs produce some activation of the receptors, as either estrogens or as SERMs.
Alkylphenols and products produced from them have come under increased scrutiny due to their association as potential endocrine disruptive chemicals. This is due to the weak estrogenic activity of alkylphenols as well as degradation intermediates of the alkylphenol products. Alkylphenols are commercially used in, for example, herbicides, gasoline additives, dyestuffs, polymer additives, surfactants, lubricating oil additives and antioxidants. In recent years, alkylphenol alkoxylates, such as ethoxylated nonylphenol, have been criticized for having poor biodegradability, high aquatic toxicity of the by-products of the biodegradation of the phenol portion. Thus, there is an increasing concern that these chemicals may act as endocrine disrupters, for example, by acting as pseudo-estrogens. Some studies have shown there to be a link between alkylphenols and declining sperm count in human males and there is evidence that alkylphenols may harmfully disrupt the activity of human estrogen and androgen receptors. Specifically, Routledge et al., “Structural features of alkylphenolic chemicals associated with estrogenic activity”, J. Biol. Chem., 1997 Feb. 7; 272(6):3280-8, compared the estrogenic activity of different alkylphenols with the naturally occurring hormone 17β-estradiol in an estrogen-inducible strain of yeast. The results indicated that optimal estrogenic activity requires a single branched alkyl group composed of between 6 and 8 carbon atoms located at the para position on an otherwise unhindered phenol ring with 4-tert-octylphenol (8 carbons also named 4-(1,1,3,3-Tetramethyl-butyl)-phenol)) having the highest activity. Routledge et al. tested various alkylphenols in the assay and indicated that alkyl chain length, degree of branching, location of the alkyl group on the phenyl ring, and degree of isomeric heterogeneity affect the binding efficiency but they were not able to draw a structure activity conclusion. For example, Routledge et al. speculated that the isomers of p-nonylphenol, which was identified to have 22 para-isomers as determined by high resolution gas chromatographic analysis, would not have similar activity. Routledge et al., however, did not elucidate which isomer or isomers were the active species. Interestingly, Tabria et al., “Structural requirements of para-alkylphenols to bind to estrogen receptor”, Eur. J. Biochem. 262, 240-245 (1999) found that when using human estrogen receptors, the receptor binding of alkylphenols was maximized when the number of alkyl carbons was nine carbon atoms. Tabria et al. noted that branched chain nonylphenol, mixture of isomers (commercially available and which did not contain any n-nonylphenol) was almost as active as n-nonylphenol.
Nonylphenol ethoxylate and octylphenol ethoxylate are widely used as nonionic surfactants. Concern over the environmental and health impact of these alkoxylated alkylphenols has led to governmental restriction on the use of these surfactants in Europe, as well as voluntary industrial restrictions in the United States. Many industries have attempted to replace these preferred alkoxylated alkylphenol surfactants with alkoxylated linear and branched alkyl primary and secondary alcohols, but have encountered problems with odor, performance, formulating, and increased costs. Although the predominate focus has been on the alkylphenol ethoxylates and the potential problems associated with these compounds (primarily with the degradation by-products), there remains a need to review other components to select combinations that have similar or improved performance benefits with reduced negative impacts.
Nonylphenol and dodecylphenol can be produced by the following steps: propylene oligomerization and separation of propylene trimer and tetramer, and phenol alkylation with propylene trimer and separation of nonylphenol, or phenol alkylation with propylene tetramer and separation of dodecylphenol. Tetrapropenyl phenol prepared from propylene tetramer has been widely used in the lubricant additive industry. Propylene tetramer comprises carbon chains with a high degree of methyl branching and an average carbon number of 12. Generally the tetramer can have a carbon number distribution between 10 to 15 carbons. The tetramer imparts oil solubility and compatibility with other oil soluble lubricant additive components. A tetramer is also a cost effective olefin to manufacture. Dodecylphenol derived from propylene tetramer is primarily used as an intermediate in the production of additives for lubricating oils, commonly sulfurized alkyl phenate detergents. To a lesser degree, these branched phenate detergents have employed some degree of linear olefin.
U.S. Patent Application Publication No. 20070049508 (“the '508 application”) discloses a lubricating oil composition containing (a) an oil of lubricating viscosity, and (b) a detergent containing an unsulfurized alkali or alkaline earth metal salt of a reaction product of (i) an olefin having at least 10 carbon atoms, wherein greater than 80 mole % of the olefin is a linear C20 to C30 n-alpha olefin, wherein less than 10 mole % of the olefin is a linear olefin of less than 20 carbon atoms, and wherein less than 5 mole % of the olefin is branched chain olefin of 18 carbons or less, and (2) a hydroxyaromatic compound. Comparative Example C in the '508 application discloses a branched pentadecylphenol calcium salt prepared by alkylating a phenol with a branched chain C14 to C18 olefin derived primarily from propylene pentamer. However, the '508 application discloses that the branched pentadecylphenol calcium salt of Comparative Example C was ineffective in preventing endocrine disruption effects. Furthermore, the '508 application does not disclose a boiling point range for the olefin.
U.S. Pat. No. 5,510,043 (“the '043 patent”) discloses a lubricating oil additive containing (a) an alkaline earth metal salt of a sulfurized monoalkylcatechol derivative and (b) a sulfurized monoalkylcatechol. The '043 patent further discloses that the sulfurized monoalkylcatechol can be obtained by sulfurizing an alkylation product of a catechol produced by reacting a catechol with an olefin such as a propylene pentamer in the presence of a catalyst. There is no disclosure in the '043 patent of endocrine disruption effects. There is likewise no disclosure in the '043 patent of a boiling point range for the olefin used in the allylcatechol synthesis.
It is desirable to develop improved lubricating oil additives derived from alkylphenols for use in lubricating oil compositions.